An ONU is a device in which optical-to-electrical conversions take place. ONU's are usually installed close to a customer's home or office and connected to central offices by optical fibers and/or copper pairs. Signals received from these optical fibers and copper pairs are converted into electrical signals that are then transmitted along electrical conductors or coaxial cables to the customers' premises.
Electrical signals, in the frequency range above the voice band, received from the customers are converted by the optical network units into optical signals which are transmitted by the optical fibers to the central office. Electrical signals in the voice band received from the customer are transmitted to the central office on the copper pairs.
ONU's are located just adjacent to the outside wiring interface at a customer site. This outside wire interface connects the ONU to the customer's line to transfer the voice, data, video, high definition broad band and XDSL signals to the customer. Because ONU's are located outside a customer's premises, they are contained in a housing, enclosure or module for protection from the weather and other external forces.
An SEM is a sealed enclosure that can be mounted in a variety of locations and protects a variety of electronics equipment from the elements. Traditional SEM designs are shown in FIG. 1 and FIG. 2.
Unfortunately, conventional mechanical designs of Sealed Expansion Modules (“SEM”) and Optical Network Unit (“ONU”) enclosures impose many deployment restrictions. As shown in FIG. 1, many legacy SEM's are installed with variable length cable spools that are difficult to ship because of the shape and design of the cable spools. These SEM's are also expensive because any cabling in excess of what is required for a given installation becomes an unnecessary expense.
As shown in FIG. 2, some legacy SEM's are deployed with factory sealed and installed, fixed length Drop/Co/VDSL/power/fiber cables solving the shipping and cost issues associated with cable spools. However, these SEM's require an additional junction box to connect the cable pigtails to the in-ground cabling, making them more difficult to install and leading to increased costs and reduced reliability due to the additional connections inside the junction box.
The fixed length cables also may restrict the distance the enclosure can be placed from the SAI or fiber junction. Alternatively, the fixed length cables require intimate knowledge of the deployment site to pre-terminate the cables to an appropriate length.
U.S. Pat. No. 5,828,807 discloses an ONU mechanical enclosure having two compartments with separate openings. One compartment houses the electronics and optics of the optical network unit, and the second compartment houses a drop terminal block or blocks of the unit. Doors cover and seal the openings when the unit is in use. The doors can be rotated upwards when the interior of the optical network needs to be accessed. Catches hold the doors in open positions to allow the technician freedom to use both hands.
U.S. Pat. No. 5,828,807 and other prior ONU mechanical enclosures insist that the dual compartment/separate enclosures are desirable because separate doors and compartments allow craftspersons to access the desired compartment without unnecessarily exposing the electronic elements in the other compartment to weather elements. The prior art ignores the additional costs associated with manufacturing dual compartments and the additional costs and logistical concerns of installing a bulkier dual compartment ONU enclosure.
These types of ONU enclosures suffer numerous other drawbacks as discussed in United States patent application Ser. No. 2003/0118312. One such drawback is that the internal environment for the electronics and optical components is not controlled. Hence, during servicing of the appropriate compartments, humidity and wind driven rain can enter the compartment and be trapped therein when the door is closed. Potential corrosion of electronic components and/or shorting out of the power supply can occur as a result.
Another drawback of existing ONU mechanical enclosures is that human error during servicing often occurs because line cards within the ONU mechanical enclosures are often mistakenly identified as damaged and accidentally exchanged. This results in unnecessary delays in returning an ONU to its intended function and may exacerbate the problem.
The technology discussed in United States patent application Ser. No. 2003/0118312 addresses these problems by providing for a housed environmentally sealed printed circuit board/line card such that environmental conditions cannot affect optical and electronic components. The printed circuit boards/line cards also are not changed individually so that an incorrect circuit board will not be replaced when the service breaks down. Instead, when problems occur, the entire environmentally sealed printed board arrangement is replaced for a new one. However, the device described in United States patent application Ser. No. 2003/0118312 still requires two separate sealed compartments for cable termination and active electronics, limiting possible installation sites and creating added installation expenses.
Hence, there is a need in the art for a convenient to install, reliable, inexpensive, durable, safe and effective SEM or module for protecting an ONU that does not require two separate sealed compartments for cable termination and active electronics and does not require expensive variable length cable spools or mounting-limiting fixed-length cables.